System and method for monitoring the life of a physiological sensor

ABSTRACT

Aspects of the present disclosure include a sensor configured to store in memory indications of sensor use information and formulas or indications of formulas for determining the useful life of a sensor from the indications of sensor use information. A monitor connected to the sensor monitors sensor use and stores indications of the use on sensor memory. The monitor and/or sensor compute the useful life of the sensor from the indications of use and the formulas. When the useful life of the sensor is reached, an indication is given to replace the sensor.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/573,332, filed Dec. 17, 2014, entitled “System and Method forMonitoring the Life of a Physiological Sensor”, which is a continuationof U.S. application Ser. No. 13/015,207, filed Jan. 27, 2011, entitled“System and Method for Monitoring the Life of a Physiological Sensor,”which is a continuation of U.S. application Ser. No. 11/580,214, filedOct. 12, 2006, entitled “System and Method for Monitoring the Life of aPhysiological Sensor,” each of which is incorporated herein by referencein its entirety.

The present application also relates to U.S. Pat. No. 6,388,240, filedMar. 2, 2001, entitled “Shielded Optical Probe and Method Having aLongevity Indication,” and U.S. Pat. No. 6,515,273, filed Feb. 10, 2000,entitled “A system for Indicating the Expiration of the Useful OperatingLife of a Pulse Oximetry Sensor,” their continuations, divisionals,continuation-in-parts and the like, and incorporates each of theforegoing disclosures herein by reference in their entirety.

FIELD

The present invention relates to a sensor for measuring oxygen contentin the blood, and, in particular, relates to an apparatus and method formonitoring the life of a pulse oximetry sensor.

BACKGROUND

Early detection of low blood oxygen is critical in a wide variety ofmedical applications. For example, when a patient receives aninsufficient supply of oxygen in critical care and surgicalapplications, brain damage and death can result in just a matter ofminutes. Because of this danger, the medical industry developed pulseoximetry, a noninvasive procedure for measuring the oxygen saturation ofthe blood. A pulse oximeter interprets signals from a sensor attached toa patient in order to determine that patient's blood oxygen saturation.

A conventional pulse oximetry sensor has a red emitter, an infraredemitter, and a photodiode detector. The sensor is typically attached toa patient's finger, earlobe, or foot. For a finger, the sensor isconfigured so that the emitters project light from one side of thefinger, through the outer tissue of the finger, and into the bloodvessels and capillaries contained inside. The photodiode is positionedat the opposite side of the finger to detect the emitted light as itemerges from the outer tissues of the finger. The photodiode generates asignal based on the emitted light and relays that signal to the pulseoximeter. The pulse oximeter determines blood oxygen saturation bycomputing the differential absorption by the arterial blood of the twowavelengths (red and infrared) emitted by the sensor.

The foregoing conventional sensor is typically detachable from theoximeter to allow for periodic replacement. Periodic replacement isadvantageous for a wide variety of reasons. For example, the sensor canbecome soiled, thereby possibly inhibiting sensor sensitivity or causingcross-patient contamination. Furthermore, the electronic circuitry inthe sensor can become damaged, thereby causing sensor failure orinaccurate results. Moreover, the securing mechanism for the sensor,such as an adhesive substrate, can begin to fail, thereby improperlypositioning the sensor in proximity to a measurement site and providinginaccurate data. Accordingly, periodic replacement of the sensor is animportant aspect of maintaining a sterile, highly sensitive, accuratepulse oximetry system.

However, a conventional pulse oximetry sensor is generally reliant on anoperator for timely replacement of soiled, damaged, or otherwiseoverused sensors. This approach is problematic not only from thestandpoint of operator mistake or negligence, but also from theperspective of deliberate misuse for cost saving or other purposes.

SUMMARY

Accordingly, one aspect of the present invention is to provide aninexpensive, accurate sensor life monitoring system for monitoring theuseful and safe life of a pulse oximetry sensor. In an embodiment, asensor is provided with a memory device, such as, for example, an EPROMor EEPROM. At predetermined intervals and/or in response topredetermined events, information is written onto the memory device.When the sensor reaches a predetermined level of use, a sensorreplacement signal is indicated to a user.

In an embodiment, depending on the characteristics of the sensor, thesensor stores information related to the life expectancy of the sensor.In an embodiment, the life expectancy information is a function or setof functions that is used to calculate the useful life of the sensor. Inan embodiment, the information is an indication of the use of thesensor. In an embodiment, the function or set of functions is stored onthe sensor with an indication of the use of the sensor. In anembodiment, the function or set of functions is used in conjunction withthe indication of the use of the sensor in order to determine the usefullife of the sensor.

In an embodiment, the function or set of functions is a predeterminedfunction or set of functions based on empirical data obtained fromobserving sensor use and/or inspecting used sensors. In an embodimentthe empirical data is obtained experimentally in the normal course ofusing a sensor on a patient. In an embodiment, the empirical data isobtained experimentally without using patients. In an embodiment, thefunction or set of functions is based on theoretical data. In anembodiment, the function or set of functions is based on the individuallife of each component of the sensor.

In an embodiment, a patient monitor works in conjunction with the sensorto determine the useful life of the sensor. In an embodiment, themonitor tracks information related to the use of the sensor and storesan indication of the information related to the use on the sensor. In anembodiment, the monitor uses the information stored on the sensor,including the functions and/or the previously stored indications of useand calculates the useful sensor life. In an embodiment, the monitorupdates the already stored indications of use on the sensor. In anembodiment, the monitor indicates a sensor life expired status to auser.

In an embodiment, the sensor uses the function(s) and/or the indicationsof use and calculates the useful sensor life. In an embodiment, thesensor calculates the useful life of the sensor based on informationprovided by the monitor. In an embodiment, the monitor stores thefunctions and/or the sensor use information relevant to a particularsensor. In an embodiment, a range or set of functions is stored on themonitor and the sensor stores an indication of which function or set offunctions are to be used to calculate the useful life of the sensor. Inan embodiment, indications of use information are stored on the sensor,so as to conserve memory space. In an embodiment, the sensor memoryincludes both read only and read/write memory. In an embodiment, theread only memory stores the functions and other read only informationsuch as the update period, expiration limit, index of functions, nearexpiration percentage, or the like. In an embodiment, the read/writememory stores use information which changes periodically based on theuse of the sensor.

In an embodiment, the use information includes one or more of thefollowing: the number of times a sensor has been connected and/ordisconnected from a monitor, the number of times the sensor has beensuccessfully calibrated, the total elapsed time the sensor has beenconnected to the monitor, the total time the sensor has been used toprocess the patient vital parameters, the age of the sensor, thecumulative or average current applied to the LED's, the cumulative oraverage current provided to the sensor, the cumulative or averagetemperature of the sensor during use, an indication of the expirationstatus or existing life of the sensor, the number of times the clip hasbeen depressed, the number of times the clip has been placed on apatient, the number of patients the sensor has been used on, the numberof times and time between cleanings and/or sterilization of the sensor,the number of monitors a particular sensor has been connected to, thenumber of times a sensor has been refurbished, the number of times thesensor has been sterilized, the time period between uses, as well as anyother information useful in determining the life of a sensor as would beunderstood by a person of ordinary skill in the art from the disclosureherein.

In an embodiment, a reusable noninvasive physiological sensor isdisclosed. The sensor has a first and second emitter which emit light ofat least two wavelengths through tissue, a detector which senses thelight after it has passed through the tissue and generates a signalindicative of the sensed light, a memory device which stores anindication of sensor use information and an indication of a function tobe used in determining the useful life of the sensor, and acommunication port which communicates at least the signal andinformation stored on the memory with a patient monitor. In anembodiment, the memory device has a read only portion and a read/writeportion. In an embodiment, the indication of the function is stored inthe read only portion and the indication of sensor use information isstored in the read/write portion of the memory. In an embodiment, thememory device is made up of a plurality of memory devices. In anembodiment, the indication of the sensor use information is anindication of one or more of an age of the sensor, a use time of thesensor, a current supplied to the sensor, a temperature of the sensor, anumber of times the sensor is depressed, a number of times the sensor iscalibrated, or a number of times the sensor is powered up. In anembodiment, the monitor tracks the use information and sends anindication of the use information to the sensor for storage in thememory.

In an embodiment, a method of determining the useful life of aphysiological sensor is disclosed, the method includes the steps ofusing a physiological sensor having a memory device to obtainphysiological information, monitoring the use of the sensor, storing anindication of the use of the sensor on the memory device, anddetermining when the useful life of the sensor has been exceeded byusing a mathematical function and the indications of use. In anembodiment, the indication of the use of the sensor includes anindication of one or more of an age of the sensor, a use time of thesensor, a current supplied to the sensor, a temperature of the sensor, anumber of times the sensor is depressed, a number of times the sensor iscalibrated, or a number of times the sensor is powered up. In anembodiment, the step of monitoring the use of the sensor is performed bya patient monitor. In an embodiment, the step of monitoring the use ofthe sensor is performed by the sensor. In an embodiment, themathematical function is stored in the sensor memory. In an embodiment,the mathematical function is stored in the memory of a patient monitor.In an embodiment, an indication of the mathematical function is storedin the sensor memory. In an embodiment, the mathematical function isderived from use data. In an embodiment, the use data is obtained fromused sensors. In an embodiment, the used sensors have been used onpatients. In an embodiment, the physiological sensor is one or more of ablood oxygen sensor, a blood pressure sensor, or an ECG sensor.

In an embodiment, a method of reusing at least portion of a sensor isdisclosed. The method includes the steps of accessing a memory device ofa physiological sensor, retrieving sensor use information on the memorydevice, and using the retrieved sensor use information determine if atleast one portion of the sensor can be reused. In an embodiment, themethod also includes the step of reusing at least one portion of thesensor. In an embodiment, the step of reusing includes producing arefurbished sensor including at least one part of the sensor. In anembodiment, the method also includes the step of analyzing the useinformation to determine an extent of use of the sensor. In anembodiment, the method includes the step of storing reuse information onthe refurbished sensor.

In an embodiment, a method of indicating when a physiological sensorneeds to be replaced is disclosed. The method includes the steps ofemitting light from a light emitting element, detecting light from thelight emitting element after it has been attenuated by tissue, storinginformation on a sensor memory module, determining when the sensormemory module is full, and indicating that the sensor needs to bereplaced when it is determined that the sensor memory module is full. Inan embodiment, the method includes the step of storing information atpredetermined time intervals. In an embodiment, the information includesusage information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a physiological measurement system.

FIG. 2A illustrates an embodiment of a sensor assembly.

FIGS. 2B-C illustrate alternative sensor embodiments.

FIG. 3 illustrates a block diagram of an exemplary embodiment of amonitoring system.

FIG. 4 illustrates a block diagram of the contents of one embodiment ofa sensor memory.

FIG. 5 illustrates a flowchart of one embodiment of a sensor lifemonitoring system.

FIGS. 6A-6B illustrate flowcharts of embodiments of sensor lifemonitoring systems.

FIG. 7 illustrates a flowchart of one embodiment of a sensor lifemonitoring system.

DETAILED DESCRIPTION

FIG. 1 illustrates an embodiment of a physiological measurement system100 having a monitor 101 and a sensor assembly 101. The physiologicalmeasurement system 100 allows the monitoring of a person, including apatient. In particular, the multiple wavelength sensor assembly 101allows the measurement of blood constituents and related parameters,including oxygen saturation, HbCO, HbMet, and pulse rate.

In an embodiment, the sensor assembly 101 is configured to plug into amonitor sensor port 103. Monitor keys 105 provide control over operatingmodes and alarms, to name a few. A display 107 provides readouts ofmeasured parameters, such as oxygen saturation, pulse rate, HbCO andHbMet to name a few.

FIG. 2A illustrates a multiple wavelength sensor assembly 201 having asensor 203 adapted to attach to a tissue site, a sensor cable 205 and amonitor connector 201. In an embodiment, the sensor 203 is incorporatedinto a reusable finger clip adapted to removably attach to, and transmitlight through, a fingertip. The sensor cable 205 and monitor connector201 are integral to the sensor 203, as shown. In alternativeembodiments, the sensor 203 can be configured separately from the cable205 and connector 201, although such communication can advantageously bewireless, over public or private networks or computing systems ordevices, through intermediate medical or other devices, combinations ofthe same, or the like.

FIGS. 2B-C illustrate alternative sensor embodiments, including a sensor211 (FIG. 2B) partially disposable and partially reusable (resposable)and utilizing an adhesive attachment mechanism. Also shown is a sensor213 being disposable and utilizing an adhesive attachment mechanism. Inother embodiments, a sensor can be configured to attach to varioustissue sites other than a finger, such as a foot or an ear. Also asensor can be configured as a reflectance or transflectance device thatattaches to a forehead or other tissue surface. The artisan willrecognize from the disclosure herein that the sensor can includemechanical structures, adhesive or other tape structures, Velcro wrapsor combination structures specialized for the type of patient, type ofmonitoring, type of monitor, or the like.

FIG. 3 illustrates a block diagram of an exemplary embodiment of amonitoring system 300. As shown in FIG. 3, the monitoring system 300includes a monitor 301, a noninvasive sensor 302, communicating througha cable 303. In an embodiment, the sensor 302 includes a plurality ofemitters 304 irradiating the body tissue 306 with light, and one or moredetectors 308 capable of detecting the light after attenuation by tissue306. As shown in FIG. 3, the sensor 302 also includes a temperaturesensor 307, such as, for example, a thermistor or the like. The sensor302 also includes a memory device 308 such as, for example, an EEPROM,EPROM or the like. The sensor 302 also includes a plurality ofconductors communicating signals to and from its components, includingdetector composite signal conductors 310, temperature sensor conductors312, memory device conductors 314, and emitter drive signal conductors316.

According to an embodiment, the sensor conductors 310, 312, 314, 316communicate their signals to the monitor 301 through the cable 303.Although disclosed with reference to the cable 303, a skilled artisanwill recognize from the disclosure herein that the communication to andfrom the sensor 306 can advantageously include a wide variety of cables,cable designs, public or private communication networks or computingsystems, wired or wireless communications (such as Bluetooth or WiFi,including IEEE 801.11a, b, or g), mobile communications, combinations ofthe same, or the like. In addition, communication can occur over asingle wire or channel or multiple wires or channels.

In an embodiment, the temperature sensor 307 monitors the temperature ofthe sensor 302 and its components, such as, for, example, the emitters304. For example, in an embodiment, the temperature sensor 307 includesor communicates with a thermal bulk mass having sufficient thermalconduction to generally approximate a real-time temperature of asubstrate of the light emission devices 304. The foregoing approximationcan advantageously account for the changes in surface temperature ofcomponents of the sensor 302, which can change as much or more than tendegrees Celsius (10° C.) when the sensor 302 is applied to the bodytissue 306. In an embodiment, the monitor 101 can advantageously use thetemperature sensor 307 output to, among other things, ensure patientsafety, especially in applications with sensitive tissue. In anembodiment, the monitor 301 can advantageously use the temperaturesensor 307 output and monitored operating current or voltages to correctfor operating conditions of the sensor 302 as described in U.S. patentapplication Ser. No. 11/366,209, filed Mar. 1, 2006, entitled “MultipleWavelength Sensor Substrate,” and herein incorporated by reference.

The memory 308 can include any one or more of a wide variety of memorydevices known to an artisan from the disclosure herein, including anEPROM, an EEPROM, a flash memory, a combination of the same or the like.The memory 308 can include a read-only device such as a ROM, a read andwrite device such as a RAM, combinations of the same, or the like. Theremainder of the present disclosure will refer to such combination assimply EPROM for ease of disclosure; however, an artisan will recognizefrom the disclosure herein that the memory 308 can include the ROM, theRAM, single wire memories, combinations, or the like.

The memory device 308 can advantageously store some or all of a widevariety data and information, including, for example, information on thetype or operation of the sensor 302, type of patient or body tissue 306,buyer or manufacturer information, sensor characteristics including thenumber of wavelengths capable of being emitted, emitter specifications,emitter drive requirements, demodulation data, calculation mode data,calibration data, software such as scripts, executable code, or thelike, sensor electronic elements, sensor life data indicating whethersome or all sensor components have expired and should be replaced,encryption information, monitor or algorithm upgrade instructions ordata, or the like. In an embodiment, the memory device 308 can alsoinclude emitter wavelength correction data.

In an advantageous embodiment, the monitor reads the memory device onthe sensor to determine one, some or all of a wide variety of data andinformation, including, for example, information on the type oroperation of the sensor, a type of patient, type or identification ofsensor buyer, sensor manufacturer information, sensor characteristicsincluding the number of emitting devices, the number of emissionwavelengths, data relating to emission centroids, data relating to achange in emission characteristics based on varying temperature, historyof the sensor temperature, current, or voltage, emitter specifications,emitter drive requirements, demodulation data, calculation mode data,the parameters it is intended to measure (e.g., HbCO, HbMet, etc.)calibration data, software such as scripts, executable code, or thelike, sensor electronic elements, whether it is a disposable, reusable,or multi-site partially reusable, partially disposable sensor, whetherit is an adhesive or non-adhesive sensor, whether it is reflectance ortransmittance sensor, whether it is a finger, hand, foot, forehead, orear sensor, whether it is a stereo sensor or a two-headed sensor, sensorlife data indicating whether some or all sensor components have expiredand should be replaced, encryption information, keys, indexes to keys orhas functions, or the like monitor or algorithm upgrade instructions ordata, some or all of parameter equations, information about the patient,age, sex, medications, and other information that can be useful for theaccuracy or alarm settings and sensitivities, trend history, alarmhistory, sensor life, or the like.

FIG. 3 also shows the monitor 301 comprising one or more processingboards 318 communicating with one or more host instruments 320.According to an embodiment, the board 318 includes processing circuitryarranged on one or more printed circuit boards capable of installationinto the handheld or other monitor 301, or capable of being distributedas an OEM component for a wide variety of host instruments 320monitoring a wide variety of patient information, or on a separate unitwirelessly communicating to it. As shown in FIG. 3, the board 318includes a front end signal conditioner 322 including an input receivingthe analog detector composite signal from the detector 308, and an inputfrom a gain control signal 324. The signal conditioner 322 includes oneor more outputs communicating with an analog-to-digital converter 326(“A/D converter 326”).

The A/D converter 326 includes inputs communicating with the output ofthe front end signal conditioner 322 and the output of the temperaturesensor 307. The converter 326 also includes outputs communicating with adigital signal processor and signal extractor 328. The processor 328generally communicates with the A/D converter 326 and outputs the gaincontrol signal 324 and an emitter driver current control signal 330. Theprocessor 328 also communicates with the memory device 308. As shown inphantom, the processor 328 can use a memory reader, memory writer, orthe like to communicate with the memory device 308. Moreover, FIG. 3also shows that the processor 328 communicates with the host instrument320 to for example, display the measured and calculated parameters orother data.

FIG. 3 also shows the board 318 including a digital-to-analog converter332 (“D/A converter 332”) receiving the current control signal 330 fromthe processor 328 and supplying control information to emitter drivingcircuitry 334, which in turns drives the plurality of emitters 304 onthe sensor 302 over conductors 316. In an embodiment, the emitterdriving circuitry 334 drives sixteen (16) emitters capable of emittinglight at sixteen (16) predefined wavelengths, although the circuitry 334can drive any number of emitters. For example, the circuitry 334 candrive two (2) or more emitters capable of emitting light at two (2) ormore wavelengths, or it can drive a matrix of eight (8) or more emitterscapable of emitting light at eight (8) or more wavelengths. In addition,one or more emitters could emit light at the same or substantially thesame wavelength to provide redundancy.

In an embodiment, the host instrument 320 communicates with theprocessor 328 to receive signals indicative of the physiologicalparameter information calculated by the processor 328. The hostinstrument 320 preferably includes one or more display devices 336capable of providing indicia representative of the calculatedphysiological parameters of the tissue 306 at the measurement site. Inan embodiment, the host instrument 320 can advantageously includesvirtually any housing, including a handheld or otherwise portablemonitor capable of displaying one or more of the foregoing measured orcalculated parameters. In still additional embodiments, the hostinstrument 320 is capable of displaying trending data for one or more ofthe measured or determined parameters. Moreover, an artisan willrecognize from the disclosure herein many display options for the dataavailable from the processor 328.

In an embodiment, the host instrument 320 includes audio or visualalarms that alert caregivers that one or more physiological parametersare falling below or above predetermined safe thresholds, which aretrending in a predetermined direction (good or bad), and can includeindications of the confidence a caregiver should have in the displayeddata. In further embodiment, the host instrument 320 can advantageouslyinclude circuitry capable of determining the expiration or overuse ofcomponents of the sensor 302, including, for example, reusable elements,disposable elements, or combinations of the same. Moreover, a detectorcould advantageously determine a degree of clarity, cloudiness,transparence, or translucence over an optical component, such as thedetector 308, to provide an indication of an amount of use of the sensorcomponents and/or an indication of the quality of the photo diode.

An artisan will recognize from the disclosure herein that the emitters304 and/or the detector 308 can advantageously be located inside of themonitor, or inside a sensor housing. In such embodiments, fiber opticscan transmit emitted light to and from the tissue site. An interface ofthe fiber optic, as opposed to the detector can be positioned proximatethe tissue. In an embodiment, the physiological monitor accuratelymonitors HbCO in clinically useful ranges. This monitoring can beachieved with non-fiber optic sensors. In another embodiment, thephysiological monitor utilizes a plurality, or at least four,non-coherent light sources to measure one or more of the foregoingphysiological parameters. Similarly, non-fiber optic sensors can beused. In some cases the monitor receives optical signals from a fiberoptic detector. Fiber optic detectors are useful when, for example,monitoring patients receiving MRI or cobalt radiation treatments, or thelike. Similarly, light emitters can provide light from the monitor to atissue site with a fiber optic conduit. Fiber optics are particularlyuseful when monitoring HbCO and HbMet. In another embodiment, theemitter is a laser diode place proximate tissue. In such cases, fiberoptics are not used. Such laser diodes can be utilized with or withouttemperature compensation to affect wavelength.

FIG. 4 shows one embodiment of a memory device on the sensor 308. Memorydevice 308 has a read only section 401 and a read write section 403. Oneof ordinary skill in the art will understand that the read only and readwrite sections can be on the same memory or on a separate physicalmemory. One of ordinary skill in the art will also understand that theread only block 401 and the read write block 403 can consist of multipleseparate physical memory devices or a single memory device. The readonly section 401 contains read only information, such as, for example,sensor life monitoring functions (SLM) 405, near expiration percentage407, update period 409, expiration limit 411, index of functions 413,sensor type or the like.

The read write section 403 contains numerous read write parameters, suchas the number of times sensor is connected to a monitoring system 415,the number of times the sensor has been successfully calibrated 417, thetotal elapsed time connected to monitor system 419, the total time usedto process patient vital parameters 421, the cumulative current appliedto LEDs 423, the cumulative temperature of sensor on patient 425, theexpiration status 427, and the number of times clip is depressed 429.Although described in relation to certain parameters and information, aperson of ordinary skill in the art will understand from the disclosureherein that more or fewer read only and read/write parameters can bestored on the memory as is advantageous in determining the useful lifeof a sensor.

FIG. 5 illustrates a flow chart of one embodiment of the read/writeprocess between the monitor and the sensor. In block 501, the monitorobtains sensor parameters from the sensor. For example, in block 501,the monitor can access the read only section 401 of the memory device inorder to obtain functions such as SLM functions 405, near expirationpercentage 407, update period 409, expiration limit 411, and/or theindex of functions 413. The monitor then uses these functions in block503 to track sensor use information. In block 503, the monitor trackssensor use information, such as, for example, the amount of time thesensor is in use, the amount of time the sensor is connected to afinger, the number of times the sensor opens and closes, the averagetemperature, the average current provided to the sensor, as well as anyother stress that can be experienced by the sensor. The monitor thenwrites this use information on a periodic basis to the sensor at block505. At decision block 507, the monitor decides whether or not thesensor life is expired based on the obtained parameters from the sensorand the use information. If the sensor's life has not expired at block507, then the system returns to block 503 where the monitor continues totrack sensor use information. If, however, at decision block 507 themonitor decides that the sensor life has expired, the monitor willdisplay a sensor life expired at block 509.

Sensor use information can be determined in any number of ways. Forexample, in an embodiment, in order to determine the life of theemitters, the number of emitter pulses can be counted and an indicationstored in memory. In an embodiment, the time period in which power isprovided to the sensor is determined and an indication stored in memory.In an embodiment, the amount of current supplied to the sensor and/orLEDs is monitored and an indication is stored in memory. In anembodiment, the number of times the sensor is powered up or powered downis monitored and an indication is stored in memory. In an embodiment,the number of times the sensor is connected to a monitor is tracked andan indication is stored in memory. In an embodiment, the number of timesthe sensor is placed on or removed from a patient is monitored and anindication is stored in the memory. The number of times the sensor isplaced on or removed from a patient can be monitored by monitoring thenumber of probe off conditions sensed, or it can be monitored by placinga separate monitoring device on the sensor to determine when the clip isdepressed, opened, removed, replaced, attached, etc. In an embodiment,the average operating temperature of the sensor is monitored and anindication stored. This can be done, for example, through the use ofbulk mass as described above, or through directly monitoring thetemperature of each emitter, or the temperature of other parts of thesensor. In an embodiment, the number of different monitors connected tothe sensor is tracked and an indication is stored in memory. In anembodiment, the number of times the sensor is calibrated is monitored,and an indication is stored in the memory. In an embodiment, the numberof patients which use a sensor is monitored and an indication is stored.This can be done by, for example, by storing sensed or manually enteredinformation about the patient and comparing the information to newinformation obtained when the sensor is powered up, disconnected and/orreconnected, or at other significant events or periodically to determineif the sensor is connected to the same patient or a new patient. In anembodiment, a user is requested to enter information about the patientthat is then stored in memory and used to determine the useful sensorlife. In an embodiment, a user is requested to enter information aboutcleaning and sterilization of the sensor, and an indication is stored inthe memory. Although described with respect to measuring certainparameters in certain ways, a person of ordinary skill in the art willunderstand from the disclosure herein that various electrical ormechanical measurement can be used to determine any useful parameter inmeasuring the useful life of a sensor.

The monitor and/or the sensor determines the sensor life based on sensoruse information. In an embodiment, the monitor and/or sensor uses aformula supplied by the sensor memory to measure the sensor life usingthe above described variables. In an embodiment, the formula is storedas a function or series of functions, such as SLM functions 405. In anembodiment, experimental or empirical data is used to determine theformula used to determine the sensor's life. In an embodiment, damagedand/or used sensors are examined and use information is obtained inorder to develop formulas useful in predicting the useful sensor life.

In an embodiment, a formula or a set of formulas is stored in themonitor's memory. An indication of the correct formula or set offormulas to be used by the monitor is stored in the sensor. Theindication stored on the sensor is read by the monitor so that themonitor knows which formula or series of formulas are to be used inorder to determine the useful life of the sensor. In this way, memoryspace is saved by storing the functions or set of functions on themonitor's memory and only storing an indication of the correct functionor functions to be used on the sensor memory.

In an embodiment, a weighted function or average of functions isdetermined based on the sensor/monitor configuration. For example, in anembodiment, the sensor life function is the sum of a weighted indicationof use, For example, in an embodiment, the following sensor lifefunction is used:

$\begin{matrix}{\sum\limits_{i}^{n}{f_{ij}c_{j}}} & 1\end{matrix}$where ƒ_(ij) refers to a function determined based on operatingconditions and c_(j) refers to an indication of sensor use. For example,the correct ƒ_(ij) can be determined from a table such as:

Cur- Calibr- Mod- Time₁ Time₂ Temp. rent ations Age el . . . . . . F₁ƒ_(1,1) ƒ_(2,1) ƒ_(3,1) ƒ_(4,1) ƒ_(5,1) ƒ_(6,1) ƒ_(7,1) . . . . . . F₂ƒ_(1,2) ƒ_(2,2) ƒ_(3,2) ƒ_(4,2) ƒ_(5,2) ƒ_(6,2) ƒ_(7,2) . . . . . . F₃ƒ_(1,3) ƒ_(2,3) ƒ_(3,3) ƒ_(4,3) ƒ_(5,3) ƒ_(6,3) ƒ_(7,3) . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .Where F_(i) refers the type of sensor and/or the type and number ofparameters being monitored. For each different sensor and for eachdifferent parameter, a separate function is used in determining theuseful life of a sensor. In an embodiment, the correct F_(i) for a givensensor can be stored on the sensor memory. In an embodiment, all of thefunction ƒ_(ij) for a sensor are stored in the sensor memory. In anembodiment, the entire table is stored in the sensor memory. c_(j) canbe determined from the monitored sensor parameters. For example, a c_(j)for can be determined by counting the total time in use, averaging usetime during certain parameters, squaring use time, etc. Thus a c_(j) canbe an indication of use. In an embodiment, the correct c_(j) for thenumber of times the sensor has been turned on or off can be determinedby the following formula:

$\begin{matrix}{\mathbb{e}}^{\frac{c}{100}} & 2\end{matrix}$where c is the number of times turned on or off.

In an embodiment, when the useful life of a sensor has been reached, themonitor or sensor sounds an alarm or gives a visual indication that thesensor is at the end of its life. In an embodiment, the monitor willgive an indication that the sensor is bad. In an embodiment, the monitorwill not output data. In an embodiment, an indication of the end of thesensor life is not given while the sensor is actively measuring vitalsigns. In an embodiment, the percent of life left in a sensor isindicated. In an embodiment, an estimated remaining use time isindicated. In an embodiment, an indication that the end of the sensorlife is approaching is indicated without giving a specific percentage ortime period.

FIGS. 6A and 6B illustrate flowcharts of embodiments of sensor lifemonitoring systems. Referring to FIG. 6A, In an embodiment of a sensorlife monitoring system, a sensor including a memory device is connectedto a monitor. The sensor transmits sensor information to the monitor atblock 601. The information can include one or more of a function, useparameters, expiration parameters, or any other sensor specificinformation useful in determining the life expiration of a sensor. Atblock 603, the sensor information is used to determine the correctfunction to use in determining the sensor expiration date. Any previoususe information transmitted is also used during the monitoring process.At block 605, the patient monitor monitors the sensor use. Optionally,the monitor periodically writes updated use information to the sensor atblock 607 or In an embodiment, the use information is written once atthe end of a monitoring cycle. At block 609, the monitor computes sensorlife parameters and sensor life expiration. The system then moves ontodecision block 611 where it is determined whether the sensor life hasexpired. If the sensor life has expired, then the system moves to block613 where an indication of the sensor life expiration is given. If thesensor life has not expired at decision block 611, then the systemreturns to block 605, where sensor use is monitored.

FIG. 6B illustrates a flowchart where the sensor life is calculated onthe sensor instead of the monitor. At block 671, the patient monitormonitors sensor use. The use information is supplied to the sensor atblock 673, the use information is recorded. At block 675, the sensorcalculates the sensor life expiration. The system then moves ontodecision block 677. At decision block 677, if the sensor has expired,the system moves onto block 679, where the sensor sends an expirationindication to the monitor and the monitor indicates the sensorexpiration at block 681. If, however, at block 671 the sensor has notexpired, the system returns to block 671 where the sensor use ismonitored.

FIG. 7 illustrates a flowchart of an embodiment of a system formeasuring the life of a sensor. In the course of monitoring a patient,information is written on the EPROM. Because the EPROM is finite in theamount of information it can hold, at some point, the EPROM becomesfull. When the EPROM becomes full, the sensor will need to be replaced.Thus, an EPROM full signal indicates that the life span of the sensorhas expired. The EPROM's memory capacity can be chosen to so as toestimate the life of the sensor. In addition, the monitor can beprogrammed to write to the sensor at set intervals so that after apredictable period of time, the EPROM's memory will be full. Once theEPROM is full, the monitor gives an audio and/or visual indication thatthe sensor needs to be replaced.

Referring to FIG. 7, the patient monitoring system determines whether towrite to the sensor EPROM at block 700. If information is not to bewritten to the EPROM at block 700, then the system continues at block700. If information is to be written to the EPROM at block 700, then thesystem continues to block 701, where the system determines if the EPROMis full. If the EPROM is full, then the system moves to block 703, wherethe system writes information to the EPROM. Once the information hasbeen written, the system returns to block 700 where it waits untilinformation is to be written to the EPROM. If at block 701, the systemdetermines that the EPROM is full, then the system moves to block 703,where an indication is given to the user that the sensor needs to bereplaced.

In an embodiment, the sensor can be refurbished and used again. Forexample, if the memory used is an erasable memory module, then thesensor's memory can be erased during the refurbishment process and theentire sensor can be used again. In an embodiment, each time part or allof the memory is erased, an indicator of the number of times the memoryhas been erased is stored on the memory device. In this way, anindication of the number of refurbishments of a particular sensor can bekept. If a write only memory is used, then parts of the sensor can besalvaged for reuse, but a new memory module will replace the used memorymodule. In an embodiment, once the sensor memory is full, the sensor isdiscarded.

In an embodiment, various parts of used sensors can be salvaged andreused. In an embodiment, the sensor keeps track of various useinformation as described above. The sensor memory can then be reviewedto see which parts of the used sensor can be salvaged based on the useinformation stored in the memory. For example, in an embodiment, anindication of the number of times the clip is depressed is stored inmemory. A refurbisher can look at that use information and determinewhether the mechanical clip can be salvaged and used on a refurbishedsensor. Of course, the same principals apply to other aspects of thesensor, such as, for example, the LEDs, the cables, the detector, thememory, or any other part of the sensor.

Although the foregoing invention has been described in terms of certainpreferred embodiments, other embodiments will be apparent to those ofordinary skill in the art from the disclosure herein. For example,although disclosed with respect to a pulse oximetry sensor, the ideasdisclosed herein can be applied to other sensors such as ECG/EKG sensor,blood pressure sensors, or any other physiological sensors.Additionally, the disclosure is equally applicable to physiologicalmonitor attachments other than a sensor, such as, for example, a cableconnecting the sensor to the physiological monitor. Additionally, othercombinations, omissions, substitutions and modifications will beapparent to the skilled artisan in view of the disclosure herein. It iscontemplated that various aspects and features of the inventiondescribed can be practiced separately, combined together, or substitutedfor one another, and that a variety of combination and subcombinationsof the features and aspects can be made and still fall within the scopeof the invention. Furthermore, the systems described above need notinclude all of the modules and functions described in the preferredembodiments. Accordingly, the present invention is not intended to belimited by the recitation of the preferred embodiments, but is to bedefined by reference to the appended claims.

What is claimed is:
 1. A reusable noninvasive physiological sensor configured to store sensor use information, the sensor comprising: a first and second emitter configured to emit light of at least two wavelengths through tissue; a detector configured to sense the light after it has passed through the tissue and to generate a signal indicative of the sensed light; a memory device configured to store at least one indication of sensor use information and at least one sensor life function, wherein the at least one sensor life function indicates to a separately housed patient monitor how to calculate a useful life of the sensor; and a communication port configured to communicate the at least one indication of sensor use information and the at least one sensor life function to the separately housed patient monitor, wherein the separately housed patient monitor calculates the useful life of the sensor using the at least one indication of sensor use information and the at least one sensor life function received from the sensor.
 2. The sensor of claim 1, wherein the memory device comprises a read only portion and a read/write portion and the at least one indication of sensor use information is stored in the read/write portion of the memory device and the at least one sensor life function is stored in the read only portion of the memory device.
 3. The sensor of claim 1, wherein the at least one sensor life function comprises one or more mathematical equations.
 4. The sensor of claim 1, wherein the at least one sensor life function includes at least two indications of use, and wherein the at least one sensor life function assigns different weighting values to each of the at least two indications of use.
 5. The sensor of claim 1, wherein the communication port communicates the at least one sensor life function to the separately housed patient monitor based at least in part on the at least one indication of sensor use information communicated to the separately housed patient monitor.
 6. The sensor of claim 1, wherein the memory device is further configured to store sensor type information and the communication port communicates the at least one sensor life function to the separately housed patient monitor based at least in part on the sensor type.
 7. A method of determining a useful life of a physiological sensor comprising a memory device, the method comprising: receiving at the sensor a signal indicative of a physiological parameter; storing at least one indication of sensor use information and at least one sensor life function in a memory device of the sensor, wherein the at least one sensor life function indicates to a separately housed patient monitor how to calculate a useful life of the sensor; and communicating the at least one sensor life function and the at least one indication of sensor use information to the separately housed patient monitor, wherein the separately housed patient monitor calculates the useful life of the sensor using the at least one indication of sensor use information and the at least one sensor life function.
 8. The method of claim 7, wherein the at least one sensor life function includes at least two indications of use and assigns different weighting values to each of the at least two indications of use.
 9. The method of claim 7, wherein the communicating the at least one sensor life function comprises selecting the at least one sensor life function based at least in part on at least one of the stored at least one indication of sensor use information and a sensor type of the sensor stored in the memory device.
 10. The method of claim 7, wherein the at least one sensor life function comprises one or more mathematical equations.
 11. The method of claim 7, wherein the communicating the at least one sensor life function to the separately housed patient monitor is based at least in part on communicating the at least one indication of sensor use information to the separately housed patient monitor.
 12. The method of claim 7, wherein the storing further comprises storing sensor type information, and wherein the communicating the at least one sensor life function to the separately housed patient monitor is based at least in part on the sensor type information.
 13. A computer-readable non-transitory storage medium storing computer executable instructions that, when executed by one or more processors of a reusable noninvasive physiological sensor including a memory device cause the reusable noninvasive physiological sensor to: receive at the sensor a signal indicative of a physiological parameter; store at least one indication of sensor use information and at least one sensor life function in the memory device of the sensor, wherein the at least one sensor life function indicates to a separately housed patient monitor how to calculate a useful life of the sensor; and communicate the at least one indication of sensor use information and the at least one sensor life function to the separately housed patient monitor, wherein the separately housed patient monitor calculates the useful life of the sensor using the at least one indication of sensor use information and the at least one sensor life function.
 14. The computer-readable medium of claim 13, wherein the at least one sensor life function includes at least two indications of use and assigns different weighting values to each of the at least two indications of use.
 15. The computer-readable medium of claim 13, wherein the computer executable instructions, when executed, cause the reusable noninvasive physiological sensor to communicate the at least one sensor life function based at least in part on at least one of the stored at least one indication of sensor use information and a sensor type of the sensor stored in the memory device.
 16. The computer-readable medium of claim 13, wherein the at least one sensor life function comprises one or more mathematical equations.
 17. The computer-readable medium of claim 13, wherein the computer executable instructions, when executed, cause the reusable noninvasive physiological sensor to communicate the at least one sensor life function to the separately housed patient monitor based at least in part on the at least one indication of sensor use information communicated to the separately housed patient monitor.
 18. The computer-readable medium of claim 13, wherein the computer executable instructions, when executed, cause the reusable noninvasive physiological sensor to store sensor type information and to communicate the at least one sensor life function to the separately housed patient monitor based at least in part on the sensor type information. 